Incinerator kilns, and especially those of the rotary type, have an outside metallic shell, usually steel, the inside of which is fully covered by a thick ceramic or refractory, usually in the form of fire bricks having a total thickness exceeding in many cases 25 cm. These kilns usually operate at a exit gas or off-gas temperature in the range of about 1,600 to 2,400.degree. F. The ceramic or refractory walls, however, are very vulnerable to erosion and corrosion, due to the hostile conditions created by the nature of incinerated materials and high temperatures, especially, if alkali metals are present. If the viscosity of slag in the kiln is adequately high, it may form a rather thick viscous coating on the refractory and thus protect it from the hostile environment. However, when the viscosity of the slag is very low, the slag contributes to the erosion and corrosion of the ceramic, both chemically because it serves as a solvent and mechanically, as it allows foreign big pieces of abrasive material to act against the ceramic walls. If the slag is viscous to the point of becoming substantially solid, or if it has never been formed as a liquid, it becomes ineffective in promoting combustion of organic matter, and also in capturing toxic heavy metals. Therefore, it is imperative that the viscosity of the slag is very carefully monitored and controlled within a range of values. Thus, one of the objects of this invention is to control the viscosity of the slag in incinerating kilns.
U.S. Pat. No. 5,301,621 (Vassiliou et al.), which is incorporated herein by reference, describes methods and devices for slag viscosity detection through image analysis of dripping slag within rotary incineration kilns.
U.S. Pat. 5,228,398 (Byerly et al.), which is also incorporated herein by reference, describes methods and devices for controlling rotary incineration kilns by determining the position of the kiln outlet at which the slag is exiting.
U.S. Pat. 5,158,024 (Tanaka et al.) discloses a combustion control apparatus for a powdered coal-fired furnace that monitors noxious substances contained within the burning waste gases, unburned substances with the ash and the power data of a pulverizing mill in order to operate the combustion furnace safely and efficiently. The combustion control apparatus infers from the current states or data optimal control amounts that will maintain within the minimum allowable ranges the noxious nitrogen oxides and the in-ash unburned substances that affect the combustion efficiency and thereby controls the combustion furnace with good stability. The combustion control apparatus qualitatively evaluates as fuzzy quantities the density data of the nitrogen oxides contained within the exhaust gases of the unburned substances contained within the ash, and the power data of the pulverizing mill. Based upon the evaluation results a fuzzy inference is formed so as to determine the optimum control amount of the two-stage combustion air ratio for minimizing the nitrogen oxides and also the optimum control amount for the fine/coarse gain separator so as to extract powdered coal of a grain size most effective for minimizing the unburned substances within the ash.
U.S. Pat. 5,010,827 (Kychakoff et al.) discloses an apparatus for detecting the presence of carryover particles in an upper region of a furnace, such as a smelt bed boiler, includes plural spaced apart detectors. These detectors monitor discrete portions of the interior of the furnace for the purpose of detecting carryover particles in such monitored portions. Signals indicative of the carryover particles are processed to obtain a count of the carryover particles. The carryover particle count may then be displayed. For example, the signals from all of the detectors may be averaged with trends and overall changes in count rates then displayed. In addition, the counts from the individual detectors may also be displayed to assist an operator in locating the source of excessive carryover particles in the furnace. An image sensor, such as a charged coupled device (CCD) detector, may be used to provide a visual display of detected carryover particles. The information on carryover particle count may be used in controlling parameters affecting the performance of the furnace directly, or indirectly by way of operator input.
U.S. Pat. No. 4,846,083 (Serbent, deceased) discloses a method for the production of a product which can be dumped or utilized, the mineral substances being subjected in a rotary kiln to a thermal treatment at a temperature at which the charge of the rotary kiln is transformed from a pasty to liquid slag phase. The composition of the charge is so selected that a slag phase is produced in which the main components, which constitute a matrix, are in the range from 60 to 72% SiO.sub.2, 10 to 30% Al.sub.2 O.sub.3 and 5 to 25% CaO+MgO, of said matrix, wherein the total percentage of SiO.sub.2,+Al.sub.2 O.sub.3+ CaO+MgO equals 100, the total of the main components SiO.sub.2, Al.sub.2 O.sub.3, CaO and MgO amounts to more than 60% on a dry and ignition loss-free basis, of the mineral matter which is charged to the rotary kiln. The slag phase discharged from the rotary kiln is cooled and the exhaust gas from the rotary kiln is purified.
U.S. Pat. No. 4,395,958 (Caffyn et al.) discloses an incineration system for processing solid, semi-solid waste material and sludge includes an incinerator unit which has a horizontally disposed rotary primary oxidation chamber and a generally vertically disposed secondary oxidation chamber which receives gaseous products of combustion from the primary chamber. Baffles within the secondary chamber provide a tortuous gas flow path through the secondary chamber. Gaseous emissions from the incinerator unit pass through a heat recovery boiler, a baghouse and a scrubber tower before being discharged to atmosphere. A control system controls rotation of the primary oxidation chamber and an auger/shredder which feeds waste material to be burned into the primary oxidation chamber. The control system may include a programmable computer for modifying the control functions in response to programmed data relating to the characteristics of material processed in the incineration system.
U.S. Pat. No. 3,693,557 (Makuch) discloses a method and apparatus for controlling additive delivery to and circulation within an air pollution control system. The system of the invention controls the scrubber recycle flow rate and additive-to-fuel delivery ratio in response to an established pH operating level in the scrubber. The established pH operating level may be varied within limits in response to the sulfur oxide content of the gas leaving the scrubber for optimum additive usage.
Japanese Pat. 60-259816, issued Dec. 12, 1985, (Yamashita) has as purpose to automatically reduce the operation in response to the amount of emission by detecting the amount of pollutant emitted. It discloses a computing device, which, upon being inputted air pollution information from an input device, performs a predetermined computation to arrive at the operation reduction rate of respective pollutant releasing installations, in response to the inputted information. That is, by respective detectors, the amount of emission of pollutants in the exhaust gas that is released from the pollutant releasing installations is detected, and its result is inputted to the computation device via an information transmission device. Further, the computation result given by the computation device, via an information transmission device, which amounts to be the operation reduction rate for each pollutant releasing installation, is transmitted to and indicated by indicators a number of indicators.
None of the above references discloses, suggests, or implies the use of alkali analysis in the off-gases of incineration kilns for slag control, and especially for preventing the slag from assuming unacceptably low values.